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Exhaust Gas Recirculation Seminar Report
Fuel in any engine is burnt with air. Air is a mixture of gases and it contains approximately 78% nitrogen and 21% oxygen. Some of the oxygen is used to burn the fuel during the combustion process and the rest is supposed to just pass through unreacted. But when the peak temperatures are high enough for long periods of time, the nitrogen and oxygen combine to form a class of compounds called nitrogen oxides, collectively referred to as NOx. These compounds are one of the chief constituents of smog, which have an adverse effect on ecological systems. They also contribute to the formation of acid rain.
NOx emissions can be reduced by lowering the cylinder temperatures. This can be done by three ways 1) Enriching the air fuel mixture 2) Lowering the compression ratio and retarding ignition timing 3) reducing the amount of Oxygen in the cylinder that inhibits the combustion process. The first two methods reduce the efficiency of combustion and so the best way is to reduce the amount of Oxygen. This is done by recirculating some exhaust gas and mixing it into the engine inlet air. This process is known as Exhaust Gas Recirculation (EGR).
The goal of Exhaust Gas Recirculation (EGR) is to reduce the amount of NOx produced. The EGR valve recirculates gases into the intake stream. Exhaust gases have already combusted, so they do not burn again when they are recirculated. These gases displace some of the normal intake charge. This chemically slows and cools the combustion process by several hundred degrees thus reducing NOx formation.
Better fuel economy and higher power with lower maintenance cost has increased the popularity of diesel engine vehicles. Diesel engines are used for bulk movement of goods, powering stationary/mobile equipment, and to generate electricity more economically than any other device in this size range. In most of the global car markets, record diesel car sales have been observed in recent years. The exhorting anticipation of additional improvements in diesel fuel and diesel vehicle sales in future have forced diesel engine manufacturers to upgrade the technology in terms of power, fuel economy and emissions. In recent year due to globalization and industrial development, transportation industries are flourishing very fast. Such industries are very much responsible for atmospheric pollution which is detrimental to human health and environment. Internal combustion engines are the main power source for the automobile vehicles which is used by transportation industries. Mostly all the diesel engines have high thermal efficiencies because of their high compression ratio and lean air-fuel operation. The high compression ratio produces the high temperatures required to achieve auto ignition and the resulting high expansion ratio makes the engine discharge less thermal energy in the exhaust. Due to lean air-fuel mixture, extra oxygen in the cylinders is present to facilitate complete combustion. Increasing diesel consumption increases the pollutant that pollutes the atmospheric air. Thus good efforts are being made to reduce the pollutants emitted from the exhaust system without loss of power and fuel consumption. Recent concern over development in automotive technology is the low environmental impact. In fact, partial recirculation of exhaust gas, which is not a new technique, has recently become essential, in combination with other techniques for attaining lower emission levels. The development of a new generation of exhaust gas recirculation (EGR) valves and improvements in electronic controls allow a better EGR accuracy and shorter response time in transient condition.
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